Optical plastic lenses are manufactured with high productivity by injecting resins into a mold. The surface reflection of an optical lens occurs at a high rate reaching a few or several percents; to avoid this, an optical thin film used to be formed by vacuum film forming or the like to thereby attain the reflection preventing effect. However, this method using the vacuum film forming involves reversing the lens after completion of forming a film on a front side thereof, and then forming a film on a back side thereof, which thus presents a problem of requiring much time.
To address this problem, in recent years, a principle of a photonic crystal which may be formed on a surface of a lens by providing fine asperities thereon and by which the surface reflection is reduced has been a focus of study. Among conceivable methods for forming fine asperities on a surface of a lens is a method which includes forming fine asperities on a cavity (hereinafter referred to also as “product forming surface”) of a mold, performing injection molding using this mold, and thereby transferring the fine asperities to the surface of the lens.
As such a method for forming fine asperities on a product forming surface of a mold, conventionally, several methods are known in the art, such as a method which includes forming fine asperities on a surface of a lens using an electrical discharge machining (e.g., see Patent Document 1). On the other hand, a method in which an object to be processed (composed of a heat reactive substrate) is illuminated with a laser beam so that fine asperities are formed is conventionally known in the art (see Patent Document 2), though this method is not a method for forming fine asperities on a product forming surface of a mold.